From: vince@offshore.ai (Vincent Cate) Newsgroups: sci.space.policy Subject: Re: Mars Colonization References: <4fd18840.0312290331.516646b9@posting.google.com> <3FF0EB05.80507@tabletoptelephone.com> <3ff19510$0$202$75868355@news.frii.net> <3FF33708.7040102@tabletoptelephone.com> NNTP-Posting-Host: 207.42.133.230 Message-ID: <9186edb5.0401011733.1f56ef7d@posting.google.com> "Paul F. Dietz" > Hop David wrote: > > He would start with bolo habs. A series of bolo habs can be used to make > > a torus. A series of tori can make a cylinder. > > This doesn't work, since the shielding in a habitat cannot be spinning > without unacceptable loads. This design would require just as much > non-rotating shielding as a torus. I have been looking at a bolo style duel-space-hotel for GEO. It does not seem like having the shielding rotating with the hotel makes for unacceptable loads for the design I am looking at. See sample #46 at http://spacetethers.com/spacetethers.html In this sample there is a 1 mil Kg hotel at each end (so 2 mil Kg total) of a 20 km tether spinning fast enough to make 1/6th G. For this I get a tether of about 16,000 Kg with a safety factor of 2. So the tether mass is about 0.8% of the combined mass of the 2 ends (16,000/2,000,000). Since they use spectra-2000 for fishing line, it seems like the tether would not be too expensive compared to everything else. So the loads do not seem like a problem. I am only looking for shielding good enough for short term tourists and staff staying less than 2 years. It seems like 50 cm of water would handle this for GEO. Is this plausible? Am I missing something? Also Dave Boll: >Though Paul's point is a good one; I underestimated the rad dangers; >this wouldn't work beyond LEO. What sort of time frame are you looking at? Like living there forever or just a trip to Mars? Would you agree that for up to maybe 2 years that GEO could be managed with 50 cm of water shielding? Please let me know if you see anything wrong on my radiation at: http://spacetethers.com/radiation.html >That was me, at http://www.daveboll.com/nasa2.html In this page why do you say that you would have to spin things down to add a new module? Why not just lower the new module from the center while things keep spinning? Hop David: >Mars has the benefit of having 38% of Earth's gravity, two orbiting >moons which can be used as stable platforms (Imagine converting Phobos >to a tether base and putting radio dishes on it so to act as a >permanent relay satelitte), and lot's of -known- and relatively >abundant and easy to extract ressources. With a high tip speed tether in LEO you could toss something to Mars, have it aerobrake to slow down and then, with very little delta-V from a rocket, land on Phobos. Because the LEO tether mass is large for a tip speed like 4 km/sec, compared to the payload, this would not be the first LEO tether to build. However, once other tethers get you to LEO cheaply, it would be doable. Since the LEO tether can pickup from a suborbital rocket, this could be a very cheap way to get things to Mars. Once you have a tether on Phobos then going to/from the surface could be easy. It sure seems like Phobos should be developed before the surface of Mars is colonized. -- Vince